The present invention relates generally to in vitro propagation of protozoan and rickettsial parasites and more specifically to novel methods for large scale propagation of Babesia parasites and production of extracellular Babesia antigen.
Babesia parasites are the causative agents of hemoclastic animal diseases on a world-wide basis. Tick-borne species of this genus are known to infect: cattle (B. bovis, B. bigemina, B. divergens, B. major); dogs (B. canis, B. gibsoni, B. vogali); horses (B. equi, B. caballi); and rodents (B. rodhaini, B. microti). B. bovis and B. microti are also known to be infective in humans.
Immunologically active agents have not heretofore generally been available for use as vaccine components in conferring immunity against infection by Babesia parasites. This has been due in large part to difficulties attending quantitative, in vitro propagation of Babesia parasites, and especially the difficulties inherent in separating immunologically significant materials (e.g., killed, whole antigenic merozoite stages of the parasite) from host erythrocyte cells and "contaminating" host cell components such as hemoglobin. Among the pertinent recent advances in the art of parasite propagation are disclosed in Trager, et al., Science, 193: pp. 673-675 (1976) and Speer, et al., Z. Parasitenk, 50: pp. 237-244 (1976). These references, respectively, described Plasmodium propagation in erythrocytes maintained under greatly reduced oxygen tension and continuous Plasmodium propagation in selected eukaryotic host cells. More recently, substantial advances in Babesia propagation were reported by one of the co-inventors herein and his co-workers in Erp, et al., Am. Jour. Trop. Med. Hyg., 27 (5): pp. 1061-1064 (1978). Briefly put, the publication indicates that Babesia may be successfully propagated in mechanically stirred erythrocyte cultures under enhanced carbon dioxide tension and that, while the parasitic propagative methods were not suited to large scale parasite production, the results were substantially better than theretofore achieved. It is worthy of note that the attempts of Erp, et al. to propagate Babesia parasites according to the Plasmodium propagation technology of Trager, et al. were unsuccessful.
The need for even better methods of Babesia propagation has recently been amplified by the discovery of specific soluble antigenic substances producible in vitro as reported in U.S. Patent Application Ser. No. 34,664, filed Apr. 30, 1979, by Miodrag Ristic and Carlos Arellano, entitled "Babesia Antigen".